Subcarrier Pre-equalization for Frequency Selective Fading in Wireless Channels
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Solution Overview
Problem
Wireless communication systems, particularly those using larger bandwidths like 5G NR, suffer from frequency selective fading due to time dispersion, leading to variations in signal-to-noise ratio (SNR) and reduced throughput, causing network congestion and increased latency, especially at mmWave bands.
Innovation Solution
Implementing subcarrier pre-equalization digital signal processing (DSP) techniques that adjust the amplitude of data subcarriers based on feedback from receivers, reducing frequency selective fading characteristics and maintaining link margins while reducing transmit power, thus improving battery life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If larger bandwidths are used in wireless communication systems, then data throughput is improved, but frequency selective fading characteristics worsen due to time dispersion
Solution Approach 1:
The patent changes the amplitude parameter of data subcarriers dynamically based on feedback from the receiver. The baseband processor adjusts the amplitude of each subcarrier to compensate for frequency selective fading, transforming the system from static to adaptive parameter control, thereby resolving the contradiction between throughput and signal quality
2Reliability
If transmit power is increased to maintain link margins, then signal quality is improved, but energy consumption increases
Solution Approach 1:
The patent applies local quality by adjusting the amplitude of individual subcarriers rather than uniformly increasing the power of all subcarriers. Only subcarriers experiencing fading are amplified, while others maintain their original power levels, thus maintaining link margins locally where needed without increasing overall energy consumption
Solution Approach 2:
The system implements a feedback mechanism where the receiver measures the quality of received subcarriers and sends this information back to the transmitter. The baseband processor uses this feedback to intelligently adjust subcarrier amplitudes, replacing brute-force power increase with precision control based on actual channel conditions, thereby maintaining reliability while conserving energy
Data Source
AI summary
Technologies to improve throughput in wireless multiple-input-multiple-output (MIMO) and single-input-single-output (SISO) systems are described. A first device includes a baseband processor with an Orthogonal Frequency Division Multiplexing (OFDM) circuitry that uses a digital multi-carrier modulation scheme that defines a set of data subcarriers, a set of pilot subcarriers, and a direct current (DC) subcarrier to communicate data in a wireless channel between the first device and a second device. The baseband processor also includes subcarrier pre-equalization logic that receives, from the second device, feedback data indicative of a frequency selective fading characteristic of the wireless channel and adjusts a first amplitude value of a subset of the set of data subcarriers to a second amplitude value. Adjusting the first amplitude value to the second amplitude value reduces the frequency selective fading characteristic of the wireless channel.